This invention relates to a safety interlock mechanism to prevent the movement of an aircraft ground power unit while an electrical cable from the ground power unit is attached to an aircraft.
Aircraft sitting at a gate or terminal will normally shut down their engines along with any internal or auxiliary power generating equipment, especially if they intend to remain at the terminal for any significant length of time, and will instead use the electrical power supplied by a portable ground power unit carried on a wheeled trailer.
The ground power unit is towed into position by a tractor or tug, and once in place, the unit is uncoupled from the tractor and its electrical cable is connected to the aircraft by plugging the cable into a receptacle provided on the aircraft. Once it has served its purpose, and auxiliary power is no longer needed from the ground power unit, the electrical cable is removed, and tongue of the trailer of the ground power unit is reattached to a tractor and the unit removed from the vicinity of the aircraft. If the unit is moved while the electrical cable is attached to the aircraft, the aircraft itself may be damaged along with the cable, the receptacle and the generator. Damage from these so-called "pull away" incidents can be avoided if some means could be provided to prevent the tow bar from being attached to the tractor or tug while the electrical cable remains attached to the aircraft.